German Patent Publication DE 3,107,745 A1 (Hinrich et al.), published on Sep. 16, 1982 discloses a freight latch for installation in the loading floor of an aircraft, for example and so constructed that a piece of freight may roll over the latch in one direction. A spring loaded latching hook can be recessed into a frame below the upper surface of the loading floor or tilted out of the frame for engaging, for example a pallet.
German Patent DE 4,210,703 A1 (Vogg et al.), published on Oct. 14, 1993 and corresponding to U.S. Pat. No. 5,356,250, (Vogg et al.) issued on Oct. 18, 1994, discloses a latching mechanism that is adjustable in its position along the loading floor of an aircraft for retooling the floor either for passenger service or for freight service. The entire latching mechanism can also be recessed under the top surface of the floor and is operable by a foot pedal.
In order to make it possible for the above described latching devices to permit the movement of a piece of freight in the X-direction, a friction reducing layer or coating is provided on the latching hook. The friction reducing coating is for example a bronze alloy layer which is rather expensive and subject to wear and tear, because, due to the motion of a piece of freight in the X-direction, the sliding friction at the contact area between the piece of freight and latch is substantial and efforts to reduce this frictional wear increase maintenance costs. Such friction should be as small as possible in order to reduce the force required for moving a piece of freight into its loading position.
Conventional YZ-latches include in addition to the so-called Z-latch hook which is effective to hold down a freight piece in the vertical direction, a Y-stop member effective in the Y-direction. The Y-stop member is a roller installed directly in the Z-hook, see for example roller (25) in FIG. 1 of German Patent Publication 3,107,745 mentioned above. The friction reduction by a roller effective as a stop in the Y-direction in combination with a friction reducing layer on the Z-hook, leaves room for improvement, especially with regard to structural simplification and expenses, and with regard to further reducing friction particularly in the Z-direction.